Flanged Rotameter Caused Pipe Weld Cracks and Gives Wrong Readings

Heavy 4” 300# flanged rotameter not only gives wrong readings but also caused pipe weld cracks in the process plant.

Article Type:Root Cause Analysis (RCA)
Category:Instrumentation
Equipment Type:Sensors
Author:S. Raghava Chari

Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.

Flanged Rotameter Problems

A 4” 300# flanged SS rotameter with body clamped pneumatic transmitter always read erratic.

The reasons are:

  1. The heavy Rotameter Assy bolts to 4” 300 # flanges welded to 6×4 reducers which are welded to the 6” carbomate plunger pump suction pipe
  2. Plunger pump delivered flow pulsations generally shake the connected piping way high; the rotameter upstream, downstream and the bypass heavy 4”x300# heavy plug valves aggravated the pipelines vibrations much more. Hence, the pipelines welds for the rotameter installation cracked and shutdown the plant often at enormous production loss
  3. The rotameter float assumes the position that produces its constant differential pressure across the float. However, the pump delivered flows instantaneous differential pressures h1, h2, ….. The rotameter needs sensing the average of h10.5+ h20.5+ h30.5+ h40.5+ … But it senses the average of (h1+h2+h3+h4+ …)0.5 actually. Hence, the inferential flow meter measured pulsating flow readings are as much as 50% erroneous and useless.
  4. The shaking pipes shook transmitter’s delicate flapper made the readings still more meaningless
  5. Often the instrument parts broke and involved excessive instrument crew efforts in a ‘no-use’ flow measurement of very poor availability
  6. Inability to hold the rotameter exactly vertical added to these problems
  7. Perennial Jacket steam leaks posed steam loss and housekeeping problems 

Author RCA Solution

The author highlighted the plant shutdowns due to the worthless rotameter system, Operations too tired of the plant shutdowns, which loaded them heavily besides lost production, reluctantly agreed the rotameter and bypass valves temporary removal, on the author agreeing to find better flow metering methods, Eventually, they forgot the flow measurement that served no purpose!             

Flanged Rotameter
Note: The image is not related to this article.

RCA solution benefits

RCA solution benefits are:

  1. Rotameter and bypass removal eliminated numerous pipelines welds.
  2. Removing the heavy block and bypass valves eliminated pipeline shakes magnification
  3. Thanks to 1 & 2 pipeline weld cracks shutdowns reduced by 85%.
  4. Thanks to much less plant shutdown (SD) improved production and less work to them, operation crew eventually did not ask for  the no-use rotameter

Author: S. Raghava Chari

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Flanged Rotameter Caused Pipe Weld Cracks and Gives Wrong Readings

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